diff options
Diffstat (limited to 'doc/src/sgml/catalogs.sgml')
| -rw-r--r-- | doc/src/sgml/catalogs.sgml | 23 |
1 files changed, 5 insertions, 18 deletions
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml index b74f6ea9f1f..7cfca6f1182 100644 --- a/doc/src/sgml/catalogs.sgml +++ b/doc/src/sgml/catalogs.sgml @@ -1,6 +1,6 @@ <!-- Documentation of the system catalogs, directed toward PostgreSQL developers - $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.95 2005/01/05 23:42:03 tgl Exp $ + $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.96 2005/02/13 03:04:15 tgl Exp $ --> <chapter id="catalogs"> @@ -289,9 +289,10 @@ </indexterm> <para> - The catalog <structname>pg_am</structname> stores information about index access - methods. There is one row for each index access method supported by - the system. + The catalog <structname>pg_am</structname> stores information about index + access methods. There is one row for each index access method supported by + the system. The contents of this catalog are discussed in detail in + <xref linkend="indexam">. </para> <table> @@ -453,20 +454,6 @@ </tgroup> </table> - <para> - An index access method that supports multiple columns (has - <structfield>amcanmulticol</structfield> true) <emphasis>must</> - support indexing null values in columns after the first, because the planner - will assume the index can be used for queries on just the first - column(s). For example, consider an index on (a,b) and a query with - <literal>WHERE a = 4</literal>. The system will assume the index can be used to scan for - rows with <literal>a = 4</literal>, which is wrong if the index omits rows where <literal>b</> is null. - It is, however, OK to omit rows where the first indexed column is null. - (GiST currently does so.) - <structfield>amindexnulls</structfield> should be set true only if the - index access method indexes all rows, including arbitrary combinations of null values. - </para> - </sect1> |